The need of people for portable information mediums has ever been increasing in recent years. In recent years, R&D has been actively conducted with respect to transparent display units. When a transparent display unit is applied with a voltage, the displayed information shown on the display is visible for a user, but when no voltage is applied, the object behind the display back is visible.
During R&D, the inventor noted at least the following problems in prior art: in the structure of an existing transparent display unit, the liquid crystal molecules are located between both polarization sheets and change the polarization direction of light by controlling the rotations of the liquid crystal molecules with applied voltages, so as to form different grey scales in cooperation with the polarization sheets, but the transmittance of the transparent display unit is greatly decreased by the existence of the polarization sheets.